(1) Field of the Invention
The present invention relates generally to external combustion engines. More particularly, this invention relates to a heat regenerative external combustion engine.
(2) Description of the Prior Art
One of the Navy's in-service torpedoes, which is of conventional design, employs an external combustion expander-type engine in conjunction with monopropellant fuel. To operate the engine, a solid initiator monopropellant fuel is first combusted in the combustion chamber, producing a hot, high-pressure, energized gas which commences drive action of the torpedo and initiates the entry of a liquid sustainer monopropellant fuel into the combustion chamber. The liquid sustainer fuel, which is at ambient temperature, enters the chamber from the forward side of the chamber. Heat which is generated in the combustion of the initiator monopropellant effects combustion of the initial quantity of sustainer monopropellant which is admitted to the combustion chamber. Further entry and combustion of the sustainer monopropellant fuel in the combustion chamber continues in a self-sustaining manner due to the high temperature and pressure in the chamber resulting from combustion of the sustainer monopropellant. Due to this self-feeding combustion mechanism, the efficiency of a conventional external combustion torpedo engine depends in part upon the amount of energy that is required in order to heat the sustainer monopropellant in the combustion chamber from ambient temperature to its combustion temperature.
There are several drawbacks to the conventional external combustion engines used in torpedoes. When a torpedo is launched at a relatively low speed from a shallow depth, the pressure in the combustion chamber is low, and as a result, unburned fuel can be carried through the torpedo engine. This results in inefficiency of operation and can lead to afterburning in the drive shaft. Furthermore, combustion of a monopropellant fuel in an external combustion engine can generate substantial noise. A loud combustion process is undesirable in a torpedo engine as it can facilitate discovery of the location of the launching vessel and the torpedo.